FIG. 3.

dotL is an essential gene on bacteriological media. dotL and dotB merodiploids were constructed and recombinants selected as described in Fig. 2 were analyzed by Southern analysis (as described in Materials and Methods). The top panel shows a Southern blot of recombinants derived from a parental dotL/ΔdotL merodiploid strain probed with a 700-bp SalI fragment of DNA adjacent to the dotL gene. Lane 1 is the wild-type strain Lp02; lane 2 is JV1003, a ΔdotL/dotL merodiploid; and lanes 3 to 16 are JV1003 plated on CYET plus 5% sucrose. All 14 strains that were selected for sucrose resistance in this fashion retained the wild-type version of dotL. In contrast, the bottom panel is a similar experiment in which sucrose resistant recombinants derived from a dotB/ΔdotB merodiploid strain were probed with a dotB-region specific probe. Lane 1 is the wild-type strain Lp02; lane 2 is JV941, a dotB/ΔdotB merodiploid; and lanes 3 to 16 are JV941 selected on CYET plus 5% sucrose. In this case, two distinct types of recombinants are observed, a finding consistent with either dotB or ΔdotB, indicating that dotB is not an essential gene.